The present invention relates to a method for making polyester carbonates. More particularly, the present invention relates to a melt condensation polymerization method involving the pre-reaction of a carbonic acid diester and catalyst with a diacid followed by the reaction of an aromatic dihydroxy compound with the reacted pre-reaction mixture.
Polyester carbonates and methods for their preparation have been studied extensively throughout the years. Polyester carbonates are thermoplastic resins that are clear and have high impact resistance. Due to their optical clarity and physical properties, polyester carbonates are used extensively in injection molding, applications. The synthetic methods commonly used to make polyester carbonates are interfacial polymerization and melt condensation polymerization.
Interfacial polymerization is a well-known process. Fontana et al., U.S. Pat. No. 4,983,706, discuss the reaction of an aromatic dihydroxy compound such as bisphenol-A with phosgene and a diacid. The diacid is incorporated into the reaction mixture to produce a polyester carbonate with melt flow such that the polyester carbonate is suitable for purposes of injection molding. Melt flow can be described in terms of viscosity. Although the polyester carbonate produced by the interfacial method provides excellent viscosity for injection molding, purposes, particulate contamination is often a problem. Additionally, the interfacial method uses a hazardous chemical, phosgene, and an environmentally hazardous chlorinated solvent.
Melt condensation polymerization is a known synthetic process which often results in less particulates found in the polymer compared to the interfacial method. Although melt condensation polymerization does not involve hazardous chemicals, the polyester carbonates made by the melt condensation polymerization process often do not have the flow properties of polyester carbonate made by the interfacial method.
In order to improve the flow properties of polyester carbonates made by the melt condensation polymerization process, different methods have been studied. Sakashita et al. (Japanese Patent No. Hei 4[1992]-345616) discuss a method for preparing polyester carbonates which incorporates aliphatic diacids directly into the polyester carbonate using a melt polymerization process. This method is only concerned with polyester carbonates which contain the aromatic dihydroxy compound, 2,2,2', 2'-tetrahydro-3,3,3', 3'-tetramethyl- 1,1'-spirobi[1H-indene]-6,6'-diol, commonly known as SBI. The melt condensation polymerization method of Sakashita et al. adds the aliphatic diacid, aromatic dihydroxy compounds and catalysts in a one-step reaction.
Methods continue to be sought to prepare high quality polyester carbonates which can be used for injection molding purposes using the melt condensation polymerization process.